Experts were surprised by the document, but noted that Mussolini's remark came in April 1938, the year before he sealed a wartime alliance with the Nazi leader.

Emma Fattorini, who is researching Pope Pius XI's papacy, pointed out that Hitler had invaded Austria shortly before Mussolini's reported remark. The Italian dictator was worried about his own borders, she said.

The Hitler-Mussolini relationship was always ambivalent, she said.

"They love each other, they hate each other, they study each other," she said.

The Vatican document describes an April 10, 1938, papal meeting with the Rev. Pietro Tacchi Venturi, in which Tacchi Venturi told the pope about his talks with Mussolini three days earlier.

According to the document, Mussolini had advised the Vatican envoy "that it would be worthwhile with Hitler to be more forceful, without half-measures; not right away, not immediately, but waiting for the most opportune moment to adopt more forceful measures, for example, excommunication."

It was not clear how the Vatican reacted.

Hitler was born into a Catholic family but as an adult did not practice the faith.

Denis Mack Smith, a Mussolini biographer, said the Italian leader often made casual suggestions of this type, reflecting his initial doubts about Hitler.

"He's not too keen on him in 1938," Mack Smith said. "Hitler actually asked Mussolini for a formal alliance in the course of 1938, but Mussolini doesn't accept this until 1939 .... He was trying to keep his distance a bit."